I tried searching but didnt find anything. I know the wiring for the MAF system is different on the 85's but I wanted to know if the MAF sensors themselves changed.

Thanks,

-Jim

 

Yes, the MAF used on 1985 models is completely different, from the control scheme to the wiring. The 1985 MAF outputs a frequency modulated (digital) signal to the ECM, whereas the 1986-89 MAFs output an analog voltage signal (0-5VDC) to the ECM. The two are not compatible, nor interchangeable.

Ironically, the MAF sensors used on the later V6 engines and on much later V8s used the digital (FM) scheme, albeit at a higher range frequency, so they are also incompatible with 1985 TPI systems.

You have a one-of-a-kind system there.

 

I scored an 85 maf from a junkyard but looks like i'm going to have to keep looking, oh well Thanks Vader, when I was searching I read most of your posts on the subject and couldnt get a straight answer about the MAF. You are a huge wealth of knowledge.

-Jim

 

Interestingly, dispite their differences, an 85 MAF will function properly on an 86-89. When I converted my 85 to the 165 ECM, I retained the original MAF. In fact, I'm currently using that same 85 MAF on my 88 GTA with no problems. Drivability is identical to the later style MAF, and the scan tool shows that the computer is receiving a correct airflow number. I can only theorize that there's some sort of input buffer on the 165 that causes the PWM signal to be smoothed out to a correct voltage level that makes the 165 happy. My guess is that this was done on purpose with the intent of using the remaining 85 MAFs and then having the ability to switch to the newer PWM style mid-stream, even though it seems that it wound up being a model-year transition instead of a mid-year transition.

However... trying to use an 86-89 MAF on the 85 doesn't work.